In Imago Relationship Therapy ("Getting the Love You Want: A Guide for Couples" written by Harville Hendrix, Ph.D) we talk quite a bit about the subject of Passion. In fact, the way we look at passion is more of a sense of experiencing "full aliveness." We say, when it comes to relationships, "Safety + Commitment = Passion."
Passion could also be any emotion experienced in intensity or in its fullness.
Imago Relationship Therapy Website
Click here to meet Carol
Carol A. MFCC